Direction finder system



H. G. BUSIGNIES ETAL DIRECTION FINDER SYSTEM Filed July 16, 1945 May 30,1950 I N V EN TORS. HE/V/ G. BLG/GN/ES ATTO BY GILBERT CLA/PK PatentedMay 30, 1950 YUNTED STATES .f

Tsar carica 2,509,208 DIRECTION FINDER srs'rEM Application July 16,1945, Serial No. 605,418

11 Claims. (Cl. 343-118) rIhis invention relates to wave signallingsystems and more especially to methods and means for deriving waves of adesired wave shape from corresponding waves of a diierent shape.

In certain of the signalling arts, for example in the art of directioniinding, it is highly important to be able to derive sharp pulsed wavesfrom original received waves of smoothly rounded or broad wave shape.Direction iinding arrangements may be roughly divided into two classes,those which operate on the null signal principle and those which employa continuously rotating Searcher or loop antenna. In the null method,slight amounts of noise voltage in the system adversely affect thereliability of the direction iinding indications because the usefuldirection nding signal is very weak near the null points. In suchsystem, it is a conventional practice to locate two points of equalvoltage on either side of the null point but far enough removed from thenull point so that an appreciably strong signal can be utilized. Thismethod is not applicable to systems employing rotating loops or the likewhich are intended to produce instantaneous indications. Therefore, theproblem of noise is still a. serious one in such rotating loop systems.

Accordingly, it is a principal object of this invention to provide animproved direction finder system employing rotating loops or otherrotating directionally sensitive pick-ups.

Another object is to provide a novel wave derivation system forproducing narrow time base pulses exactly at the instants when thedirection finder signals from the rotating pick-up are at their minima.

Another object is to provide a novel wave shaping system whereby broadtime base signal waves can be converted into sharp and narrow time basepulses in exact time synchronism with the occurrence of the minima ofthe original waves.

Another object is to provide an improved indication control fordirection finder systems of the rotatable loop type using a cathode raytube indicator, whereby the control potential applied to the indicatoris in the form of a series of sharp narrow time base pulsesnotwithstanding that the wave form of response of the loop Vsignal is ofthe broad time base type.

A feature of the invention relates to a novel circuit arrangement forderiving narrow time base control pulses from original wide time baseWaves and with the pulses accurately time phased with respect to theoriginal waves.

Another feature relates to a wave shape or derivation system employing aharmonic lter which is correlated and synchronized with remaining partsof the system.

A further feature relates to a Wave shaping or derivation systememploying in circuit sequence a harmonic iilter, a low-pass lter, a wavelimiter and a wave diiierentiating network for deriving sharp pulsesfrom original wide time base signal waves.

A still further feature relates to the novel organization, arrangementand relative interconnection of parts which cooperate to produce animproved wave shaping circuit employing a harmonic lter.

Other features and advantages will be apparent after a consideration ofthe following detailed descriptions and the appended claims.

In the drawing which represents one preferred embodiment:

Fig. l is a schematic circuit diagram of a rotating loop direction lndersystem embodying the invention; r

Figs. la to 1g are a series of curves which are correlated with certainparts of Fig. 1 to be explanatory thereof.

In Fig. 1, there is shown a rotatable direction finding antenna i whichmay be of any wellknown kind, for example in the form of a loop which isarranged to be rotated at a predetermined speed by means of motor 2. Thedirection nding signals picked up by loop I as it rotates, are appliedthrough a suitable brush and commutator arrangement 3, to the input ofany wellknown direction finder radio receiver ll. When the loop is in acertain position with respect to the arriving wave front, the detectedsignals in the output of the receiver 4 will undergo minima, and thegeneral wave shape thereof will be as indicated in Fig. 1a.

If an instantaneous indicator such as a cathode ray tube oscilloscope isused to produce the directional indications at the instants ofoccurrence of the minima, it is necessary to convert the broad time basewaves of Fig. la into sharp pulses or narrow time base waves such asshown in Fig. 1g, and at the same time it is necessary to insure thatthese sharp pulses occur exactly at the instants of the minima in theoriginal detected waves (Fig. 1a.).

In order to achieve these results, the detected waves from receiver 4are applied to a harmonic filter 5 such as disclosed in applicationSerial No. 591,894, led May 4, 1945, now abandoned, to which applicationreference can be had for a detailed description of several embodimentsof a harmonic filter that may be used. This i'llter comprises forexample, a bank of energy storage elements such as electrostatic:condensers 6 which have their corresponding plates or terminalsconnected to respective individual commutator segments 1, and the'othercorresponding.' plates or terminals are connected to a common groundedbus bar 8. A pair of brushes 9, I0', make contact with the commutatorsegments, the brushes being spaced so as to provide required time delaybetween charge and discharge of ther condense'rs.' It will be understoodthat the brushes yand com'a :mutator segments undergo relativerotational" displacement so that the condensers arefcon'nectedsuccessively and cyclically inra char-'ging cir` cuit through brush 9 tothe receiver 4. Likewise, the condensers arerconne'cte'd' successivelyand cyclically in a discharging circuit through brush I0 leading to anamplier tube II. For

this.purpose, the commutator which carries-segments 'I maybe stationary;while the brushes 9" and I0 are insulatingly connectedftogether'androtated as a unit around the commutator.` In

accordance with one phase of the invention, the

rate of rotation of the brushes is synchronizedwith the rotation of loopI. For 'this purpose, the

loop driving motor'2- can be connectedsthrough suitable -transmissiongearing-I2 to the vshaft"- which carries the brushes 9 and I0,whichshaft is;` schematically represented by the ,dotted line.

Preferably, an adjustable resistor I3 is'conneoted-l betweenY receiverV4 and brush 9-to controljthe*l charging rate'to theY condensers 6'.yThe b rush' I0 is returned to ground through a high'rresistance I4 soas-not to affect the storage.' time of the energy in the variouscondensers- Withsuch a harmonielter'thegeneral character.V 'of the wavesapplied'from brushY I tothe 'control grid of amplier tube I I isrepresented' infFig. 1b;

The wave form 'in theoutputof the harmonic filter 5 will not exhibitsharp nulls, because of the"-V presence of any noise voltages as'wellasf-be-r cause of the iinitel size of then commutatorV seg'- ments 'I.Furthermore, therev is presenta cerf tain amount of commutator ripple.

Inorder to eliminate the ripple'-andi reduce the? noise content, the!waves'` from vthe output'of" tube II are applied to a lowepassy lterI5', *so* that there existsat the output of-` the said lter" I5v avwaveshape vsuch as represented in Fig." '1`c.. Filter I5 inadditionto'roundin'g o'ut'themillssomewhat', also introduces.v aI time'delay *inthe wa-ve' form. We havefound'that this time! delay can becorrected' by" a slight' displacementof one of the brushes '9,10-asfindicate'dat IDA; The` output Vof 'filter I5 issubstantial-ly'noiseLree-landVV is applied'V to awavedifferentiating-networkjcom-t prising condenser I'I and' resistorYI8, "so"th'at the-1 points P of zero potential of the 'resultantfdifer aentiated" waveV along the positive 'slopes'thei'eoh correspond in Vtimeyexactly7 to the correspondingminima' ofthe original waveior'rhfV(Figlfla'.

The wave vof Figld is then' fapp'liedtoa suitable amplierjtube ISWh'oseourtputjisappliedl to any well known fornioff'symmetrical4peakliinciter: comprising, for example; a pairno'f `grid{control-ied-"Vtubes 2!! and 2 I which" are'A arranged fto square upf the' waves fromtubeIBito render them syrrfrnet rical around the exact points of zerointerceptasf represented by'Figrle' l w The squared waves Yfromlthedoubletube limiter-f 20,'2I, are then applied,l asindicatedfbyf-Figlijf, toa cathode'f'ollower tube 2-2 haying'fa cathode@resistorV 23.' Thusa low impedance input fiss'up-V plied to the wavedifferentiating network consisting of condensers 24 and 25. Thereappears at the output of this network 24, 25, a series of very narrowtime base positive pulses (Fig. 1g)

5 which are in exact time coincidence with the corresponding minima ofthe (Fig. 11a).

The pulses of Fig. 1g. can then be applied to the control grid 26 of acathode ray tube oscillooriginal detected waves scope I6, and the grid26 can be suitably biased so that a luminous spot is not produced on thefluorescentv screen of the tube I6 except when the rpositive pulsesofFig. 1g are applied to grid 26.Y

' In order to 'indi-cate direction, the usual coordinatedeflector'pla'tes or elements 21, 28, of the cathode ray tube,r aresupplied with beam deiie'cting potentials from a suitable two-phasesweep voltage generator 29 of any well-known construction,Y whereby thecathode ray beam is caused to follow. a circular trace'on the screen oftube I5. In accordance with the presen-t in-f vention, the generator2f9`has its control member coupled by a suitable shaft to the motor I2so that the cathode ray'beam rotates in-synchronism with the rotation ofloop I.` It willbe understoodV of course that the generator 29-may beanelectronic tube generator or oscillator, the frequency Y Ycontrol-eiement of which is locked-'electrically or l electro-mechanically "tothe lmotor 2.

If the loop I is rotated-at more ytha-n 10 Rf?. S., there will beproduced ten ormore `pulses Ysuch as those ofv Fig. 1g', and because ofthe-persistencyrof normal vision, a single spot will appear on the iscreen of' the'cathode raytube andthe position of thisspotwillfcorrespond exactly vviththeposi-V tion of loop lythusgivingadirectional indication of the sourcerwhose directionis vto bedetermined.`

It willbe understood" of course, that the in-Y vention is notlimited Ytothe usev ofV an indicator of the cathoderay tube type. 'Furthermoratheindication'is not-necessarily limitedvto a circular trace. For example,theisignalfrfrom the differentiating network 24, 2 5, instead ofbeingapplied l to the control grid 25;,l canvfbe superimposed onone ofthe deector plates 21,128. YWith this typeof indication, a continuousluminous circle can be traced and a radial displacementv of'thetracewill occur in synchronism with the positions of-` the loop I when it isparallel to the arrivingwaver front. Y

Various changes and modifications can be made without departing from thespirit and scopeV of the invention.

What Vis claimed is: Y l A, ,Y

l. A direction finder system comprisingY aro-j tataoleloop antenna; adirection 'ndng-i radio receiver, a harmoniciter connected to the out-vput of said receiver, a lo'w-passnlterf connectedA to saidharmonicdilter,.means to adjust the har-r monic lterioicompensate forwave delay in said;l

low-pass filter, means to convert the signals from the lowpass filterinto narrow time base pulses, and a direction indicator Ato whichsaidpulses are applied.

charging circuit: recurrentlv and cyclically4 conne'cted'to saidlow-pass lter,rand means for vsyn-A chronizin'g saidchar'ginganddis'charging circuits with the rotation of' said loop.

3. A direction riderfsystemaccording tol claim.

1 in which said indicator comprises a cathode-ray tube, a sweep voltagegenerator connected to the deecting elements of said tube, means tosynchronize said generator with the rotation of said loop, and means tosyncronize said harmonic iilter with the rotation of said loop.

4. A direction finder system having in operative sequence a rotatableloop antenna, a radio receiver, a harmonic filter, a low-pass filter, awave squaring device, a squared-wave diiierentiating device forproducing narrow time base pulses therefrom, a cathode-ray tube to whichsaid pulses are applied, and means to synchronize the looprotation withthe harmonic iilter and with the beam deection of the cathode-ray tube.

5. In a direction iinder system, a cathode-ray tube indicator, atwo-phase sweep generator for causing the beam of said tube to trace acircular path, means to receive direction finding signals in the form ofbroad time base waves having recurrent minima, means including arotatable harmonic lter and a Wave differentiating network forconverting said signals into narrow time base pulses exactly incoincidence with said minima, and means to apply said pulses to a beamcontrol electrode of said tube.

6. A direction finder system according to claim 5 in which means areprovided to synchronize the rotation of the loop with said sweepgenerator and with said harmonic lter.

7. A wave derivation system for converting broad time base waves havingrecurrent voltage minima into narrow time base pulses in exactcoincidence with said minima, including a harmonic iilter of the typehaving a series of electric storage elements adapted to be recurrentlycharged under control of diierent portions of said Waves, andrecurrently discharged, a lowpass lter to which the discharge energy isapplied, a differentiating network connected to the low-pass lter tocause alternate zero intercepts of the waves therefrom to be in exactcoincidence with said minima, means to convert the waves from saiddifferentiating network into squaretopped waves, and a second wavediierentiating network for converting said square-topped waves intonarrow time base pulses in exact coincidence with said minima.

8. A wave derivation system according to claim 7 in which said harmonicfilter includes a segmented commutator with the segments individuallyconnected to the storage elements and a pair of brushes for contactingwith said commutator, one of said brushes being connected to thecharging circuit and the other brush being connected to the dischargingcircuit.

9. A wave derivation system according to claim 7 in which means areprovided to produce said broad time base waves. and means to time thecharging and discharging rate of said storage elements with the rate ofrecurrence of the minima of said broad time base waves.

10. In a direction finding system, a rotatable searching pick-upantenna, radio receiver means to detect direction nder signals picked upby said antenna, said detected signals having repeated voltage minimaand being of broad time base wave shape, a direction finding indicatorof the type which produces instantaneous indications, means to convertsaid signals into narrow time base pulses in exact time coincidence withsaid minima, and means to apply said pulses to said indicator to controlthe direction iinding indications thereof, said converting meansincludes a harmonic filter of the type having a plurality of energystorage elements which are recurrently and cyclically charged anddischarged.

11. tIn a direction finding system, a rotatable searching pick-upantenna, radio receiver means to detect direction nder signals picked upby said antenna, said detected signals having repeated voltage minimaand being of broad time base wave shape, a direction nding indicator ofthe type which produces instantaneous indications, means to convert saidsignals into narrow time base pulses in exact time coincidence with saidminima, and means to apply said pulses to said indicator to control thedirection finding indications thereof, said converting means includes aharmonic filter of the type having a series of electric storage elementsarranged to be recurrently and cyclically charged under control of saidsignals, and arranged to be discharged recurrently and cyclically, andmeans to synchronize the said charging and discharging rate with therate of rotation of said antenna.

HENRI G. BUSIGNIES. GILBERT R. CLARK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,851,092 Fetter Mar. 29, 19321,933,219 Nakajima et a1. Oct. 31, 1933 2,183,746 Hyland Dec. 19, 19392,186,268 Pakala Jan. 9, 1940 2,188,611 Norton Jan. 30, 1940 2,230,160Lehmann Jan. 28, 1941 2,272,607 Higgonet Feb. 10, 1942 FOREIGN PATENTSNumber Country Date 468,918 Great Britain July 15, 1937 635,793 GermanySept. 28, 1936 881,292 France Jan. 22, 1943

